Lectures

Measurements of Volume, Temperature and Numbers

by Jared Rovny
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    00:01 Next, let's go to volume.

    00:02 Something to know about volume, is that when we're discussing system of any human scale, a meter especially a meter cube is very, very big.

    00:10 It's way too big a unit for any sort of tabletop or lab experiment.

    00:14 So we very typically, I will be using smaller units of our volumes.

    00:18 For example, we might be using a cubic centimeter, where centimeter of course is one 100th of a meter, so a cubic centimeter is much smaller.

    00:27 Or for a slightly larger unit we could maybe use a thousand cubic centimeters and that is called one liter.

    00:33 And when you're looking at this, be careful not to be confused by what we have here.

    00:37 You might be tempted to think initially that 1.000 cubic centimeters might be a cubic meter or maybe 10 cubic meters.

    00:45 But remember that we're talking about cube units, not linear units.

    00:49 Which means that one meter cube is in fact a million cubic centimeters, which you can see from our picture.

    00:56 In fact the cubic meter is many, many, more cubic centimeters than a liter is.

    01:02 Now, let's discuss temperature.

    01:04 What we're going to do is first think about what temperature is? Where does temperature arise from? If we sort of zoomed in what we could do is take a look at a picture like the one we have on the right here.

    01:14 And imagine all these particles moving around and bouncing off of each other and off the walls of whatever container that they're in.

    01:20 So what we do to define a new unit of temperature is define what's call a Kelvin scale for temperature.

    01:27 And this is very simply to say that we define zero Kelvin, where our zero of temperature to it'll be the point at which all the particles as we have written on the bottom here had stopped moving.

    01:39 They are not moving anywhere anymore, and so we define this point to be our zero of temperature.

    01:43 This absolute scale the absolute zero occurs at -273.150 degrees Celsius which means that to define our Kelvin scale we need to shift our system.

    01:56 We need to shift it so that this point is what we call zero.

    02:00 To do this what we would do is literally to shift it by this exact number.

    02:04 So we say that the temperature in Kelvins will be the temperature in Celsius plus this number, this number 273.15.

    02:13 Also, very importantly since all we've done is shifting our Celsius scale.

    02:18 We haven't multiplied it by any scaling numbers or anything like that.

    02:21 The size of what we would call a Kelvin is the same size as a degree Celsius.

    02:27 And for example this would not be the case for a comparison for example between Celsius and Fahrenheit.

    02:33 A degree Fahrenheit and degree Celsius are actually different in size, whereas a degree Kelvin which we actually simply call it Kelvin rather than a degree Kelvin, is the same size as a degree in Celsius, and we'll be using this fact later on.

    02:48 Lastly, our last way of measuring thing is to ask how much of this thing is there or how many molecules of this gas do we have.

    02:57 What we do to define the number of molecules is as you might expect there are many, many molecules and one gram of a substance.

    03:06 If I look at a gram in my hand there'll be some powder or something and there are many, many, many atoms and many molecules of substance and something that is big enough that we could actually see it.

    03:16 So instead of just counting the number and using this very, very large number.

    03:20 What we do is we define a new unit call a mole.

    03:24 And we define a mole as a number of carbon 12 atoms to make up 12 grams of actual macroscopic visible substance.

    03:34 The number I've been referring to this very huge number that it takes to make up anything that's big enough to be seen is 6.022 times 10 to the 23rd objects.

    03:47 So this unit of mole is just measuring numbers.

    03:50 It's just a number of object, it doesn't have any physical unit like meters or anything like that. It's just a number.

    03:56 So I could say for example a mole of apples or a mole of plants and just be measuring a huge number of any object.

    04:03 To get a sense for how big this number is, it's actually more than a number of grains of sand that exist on the earth.

    04:10 Which means that if you have one gram of substance on your hand and you're looking at it, the number of particles in there if it's one mole will be this astronomically humongous number and so keep in mind the sense of exactly the scale things because again a mole is quite big.

    04:26 So that you are able to use this very practically something that you will need to know is that the way the periodic table is often written is to give the element name for example we have carbon and nitrogen and oxygen listed here.

    04:39 And then below the element name to list, how many grams of that atom would be in one mole of that atom? For example, we have here carbon, if I took one mole of carbon, just scoop it up from the earth somewhere, the number of grams in that mole of carbon would be 12.01.

    04:59 And just be careful here it might seem confusing we said that we define a mole based on carbon so why isn't there exactly 12 grams and one mole of carbon.

    05:09 And the reason for this is simply that if I did scoop up some carbon just from around me and what we would call natural abundance just from the earth.

    05:17 Some of that carbon would not be carbon 12, it would be an isotope carbon 13 just slightly heavier.

    05:22 And so we define moles based on carbon 12 this particular atom so that the actual carbon and its natural abundance would be slightly heavier if we took an entire mole of that carbon.


    About the Lecture

    The lecture Measurements of Volume, Temperature and Numbers by Jared Rovny is from the course Gas Phase.


    Included Quiz Questions

    1. 1 million cubic centimeters
    2. 1 liter
    3. 10 liters
    4. 1 thousand cubic centimeters
    5. 100 liters
    1. 298.15 K
    2. 98.15K
    3. 198.15 K
    4. 48.15 K
    5. -98.15 K
    1. 6.022 × 10²⁵
    2. 6.022 × 10²⁴
    3. 6.022 × 10²³
    4. 6.022 × 10²²
    5. 6.022 × 10²¹
    1. 100 mol
    2. 1000 mol
    3. 10 mol
    4. 1 mol
    5. 6.022×10²³ mol

    Author of lecture Measurements of Volume, Temperature and Numbers

     Jared Rovny

    Jared Rovny


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